Satellite communications are expanding to cover substantially different frequency bands including C, Ku, X and EHF. There are now both military and commercial satellites operating on these different frequency bands. It has become important in the military environment, and may become important in the commercial environment, for a single operator to communicate through satellites at substantially different frequency bands. This becomes a particular problem because it is often necessary to change feeds for operation at different bands. This is generally time-consuming and difficult, and in some circumstances, such as aboard ship, it is also dangerous. Thus, there has developed a need for satellite communication antenna systems which can operate at multiple bands without the need for manually interchanging feeds.
One approach to this problem is the use of a dichroic surface which separates the two bands that must be used. A dichroic surface is electromagnetically transparent to one band but opaque to the other band. The use of a dichroic reflector has the advantage that both bands can be operated simultaneously, but this is gained only at the expense of additional insertion loss in each band due to the non-ideal nature of the dichroic surface. Further, it is very difficult to design a dichroic surface with low-loss characteristics and the necessary high efficiency needed for satellite use.
A further approach is to utilize multiple feeds that are mechanically moved into position as needed. However, this requires the use of either flexible transmission lines or complex mechanical joints, both of which are expensive and difficult to use.
Therefore, there exists a need for a satellite antenna configuration which can operate at multiple bands with high efficiency, rapid transition from one band to the other and relative mechanical simplicity.